The separation of many classes of compounds by selective adsorption on molecular sieves or zeolites as well as other adsorbents is well known. For example, as disclosed in U.S. Pat. No. 4,048,205, methyl esters of fatty acids of various degrees of unsaturation may be separated from mixtures of esters of saturated and unsaturated fatty acids with X or Y zeolites exchanged with a selected cation. Further in U.S. Pat. No. 4,353,838 it is disclosed that monoethanoid fatty acids may be separated from diethanoid fatty acids with cross-linked polystyrenes, e.g. "Amberlite". The refining of oils by admixing them with magnesium silicate to adsorb coloring matter and free fatty acids from glyceride oils is disclosed in U.S. Pat. No. 2,639,289. The separation of monoglycerides from di- and triglycerides by adsorption on X or Y zeolites with desorption by a ketone was disclosed in my pending application Ser. No. 898,300, filed Aug. 20, 1986. The process for separating a mixture of triglycerides, based on the iodine values, is shown in Logan et al. U.S. Pat. Nos. 4,277,412 and 4,284,580 in which permutite and aluminated silica gel adsorbents, respectively, can be used. Also, Logan et al. U.S. Pat. No. 4,297,292 discloses fractionating triglycerides according to their iodine value with a macroreticular strong acid cation exchange resin.
The process of separating diglycerides from triglycerides described herein has many potential uses, for example, in treating oils, such as palm oil and palm olein. Diglycerides are undesirable because they adversely affect the purification of triglycerides by crystallization. Jacobsberg et al., Studies in Palm Oil Crystallization, J. A. Oil Chem. Soc., Vol. 53, October 1976, pp. 609-617. A process which separates diglycerides from triglycerides can improve the purity and recovery of such crystallizations. Another application of my separation process results from the use of diglycerides as emulsifiers in large amounts in the food industry. Mixtures of di- and triglycerides can be produced by reaction of glycerol with triglycerides or with free fatty acids, separation of the resulting mixture yields the desired diglyceride.
Another important application of my separation process resides in its utility in the synthesis of triglycerides. Cocoa butter, for example, is a high value natural product consisting predominantly of a mixture of particular triglycerides where the 2-position of glycerol is esterified with an oleyl group and the 1- and 3-positions are esterified with either the palmitoyl or the stearyl group. When the 1 and 3-positions are esterified with palmitoyl groups, the triglyceride is referred to as "POP". Likewise, when a stearyl group occupies both 1-and 3-positions, the compound is called "SOS", and when 1- and 3-positions are filled by one palmitoyl and one stearyl group, the compound is referred to as "SOP". Cocoa butter is a predominant component in chocolate confections. It is believed that large quantities of these particular triglycerides could be synthesized and used as cocoa butter extenders by reacting the appropriate 1,3-diglyceride with oleic acid, and then separating the resulting mixture of di- and triglycerides. The process of the instant invention can be used to accomplish this by separation of glyceride mixtures which contain 1,3-diglycerides, obtaining the desired 1,3-diglycerides in the extract and triglyceride in the raffinate. The 1,3-diglycerides can then be recycled to the reaction step.
I have discovered combinations of zeolites and desorbents which separate the diglycerides and triglycerides. The diglycerides are adsorbed in preference to triglycerides and are concentrated in the extract. The triglycerides, therefore, are removed from the mixture of diglycerides and triglycerides and are concentrated in the raffinate of the adsorptive separation apparatus.